This invention generally relates to a method for isolating oleic acid and producing lineloic dimer/trimer acids. More particularly, it concerns a process for reacting fatty acids which contain poly- and monounsaturates and then selectively polymerizing the polyunsaturates to produce the lineloic dimer/trimer acids.
Oleic acid, a C-18 monounsaturated carboxylic acid, is widely used as the substrate for derivatives such as soaps, esters, amides, and polymers in applications such as surfactants, lubricants, corrosion inhibitors, and polyamide production. Use of oleic acid has an advantage over saturated acids in low temperature applications and has an advantage over mixtures with polyunsaturates owing to greater oxidative stability.
Oleic acid can be isolated from animal or vegetable sources via solvent extraction as taught in U.S. Pat. No. 2,421,157 to Myers et al.; U.S. Pat. No. 2,450,235 to Gee et al. and an article entitled xe2x80x9cPreparation of oleic acid at 99.5% purityxe2x80x9d by Fremont et al. (Ann.Biol. Anim. Biochim, Biophys, 1973, 13, 691-7). Oleic acid can also be separated from other fatty acids with the use of molecular sieves as disclosed in U.S. Pat. No. 4,511,514 to Cleary et al. As disclosed in articles entitled xe2x80x9cSynthesis of oleic acid from fatty acids of tall oilxe2x80x9d by Chernova et al., (Khim.Khim.Tekhnol., 1996, 39, 74-7) and xe2x80x9cA process for stearic acid and oleic acid from castor oilxe2x80x9d by Lakshminarayana et al. (J. Oil Technol. Assoc. India, 1990, 22, 77-9), oleic acid can also be obtained from tallow or vegetable fatty acid sources by hydrogenation processes. These known processes involve multistage equipment and are typically very costly.
Other known methods have involved the use of catalyst systems to conjugate the olefins of polyunsaturated components within a fatty acid mixture providing a boiling point separation allowing an oleic acid-rich fraction to be distilled away from other components. Such methods are shown in U.S. Pat. No. 3,157,629 to Patrick; U.S. Pat. No. 3,923,768 to Powers et al.; and U.S. Pat. No. 4,271,066 to Matsuo et al. Other processes as described in U.S. Pat. No. 3,528,959 to Patrick et al.; U.S. Pat. Nos. 3,753,968 and 3,860,569 to Ward.; U.S. Pat. No. 3,980,630 to Ishigami et al.; and U.S. Pat. No. 4,659,513 to Correia, call for disproportionation of tall oil fatty acids at elevated temperature with various iodine catalyst systems. These processes require extended reaction times at elevated temperatures and large amounts of catalyst that causes isomerization of most of the oleic acid. Yields from these processes also suffer since undesired polymerization leaves dark-colored byproducts.
Another known method for isolating oleic acid from tall oil sources calls for forming an adduct of the conjugated diunsaturates in a Diels Alder protocol followed by distillation to separate a fraction rich in oleic acid. The use of stoichiometric amounts of dienophiles is required in this protocol to react with the diunsaturates which result in oleic acid as a byproduct and a C-21 diacid as the main product. U.S. Pat. No. 4,156,095 to Jevne et al.; U.S. Pat. No. 5,194,640 to Cosgrove et al. and in an article by McSweeney et al. Tall Oil and Its Usesxe2x80x94II, (Pulp Chemicals Association, NY, N.Y., 1987, p.33) are representative as disclosing such processes.
The present invention overcomes the disadvantages of the prior art processes by providing selective dimerization of linoleic acid in the presence of oleic acid from various fatty acid sources, preferably tall oil fatty acids. The process allows for the recovery of oleic acid from tall oil by first conjugating the diunsaturates followed by selective dimerization of these diunsaturates using either clay catalysis or t-butyl peroxide. Separation procedures such as distillation, then affords an oleic acid-rich fraction along with a C-36/C-54 co-product. By controlling reaction conditions, the diunsaturate content in the oleic acid obtained by this process can be very low, typically less than 10%, or between 10-15% depending on the desired application. The degree of isomerization of the oleic acid to elaidic acid and other isomers has also been minimized in the invention process. The C-36/C-54 co-product has characteristics of typical fatty acid dimer/trimers and can be used to produce polyamides/polyesters.
Thus, it is a general object of the invention to provide a process for isolating oleic acid and producing lineloic dimer/trimer acids by reacting fatty acids which contain poly- and monounsaturates and then selectively polymerizing the polyunsaturates.
Another object of the invention is to provide a process for obtaining a fatty acid from tall oil with oxidative stability and low temperature properties greater than tall oil.
It is another object of the invention to provide a process which can be modified to allow for isolation and separation of oleic acid fractions having different characteristics and properties.
A specific object of the invention is to provide a C-36/C-54 product which is useful in a number of applications including polyamide and polyester production.
Another specific object of the invention is that the yield of this process is quantitative less mechanical losses. No product is lost because the separation process involves no recyclables or heads/bottoms removal.
In the present invention, these purposes, as well as others which will be apparent, are achieved generally by providing a process for isolating oleic acid and producing linoleic acid-based dimer/trimer acids by first conjugating polyunsaturated components of fatty acids in the presence of monounsaturated components and then selectively polymerizing the polyunsaturated components to produce the dimer/trimer acids.
The fatty acid starting material includes monounsaturated components such as oleic acid, oleic acid isomers and non-conjugated linoleic acid. In general, the fatty acids used in the invention process are selected from tall oil fatty acids, vegetable fatty acids, animal fatty acids and marine fatty acids.
In the first process step, the fatty acids are treated with iodine and the mixture is heated to conjugate the polyunsaturated components. The amount of iodine in the conjugation reaction ranges from 0.01 to 0.15% by weight of the fatty acid. A co-catalyst may be further added to the mixture to enhance the conjugation of the polyunsaturates. Preferably the co-catalyst is selected from the group consisting of iron complexes, iron powder and bromine. In an alternate process embodiment, iron-iodine, FeI2. itself can be used as the catalyst in amounts of approximately 0.2%. In any instance the mixture is heated to temperatures in the range of 200 to 260xc2x0 C. for up to 6 hours to complete the conjugation reaction.
After the conjugation reaction, material is added to the mixture to cause polymerization of the conjugated polyunsaturated components and subject to further heat treatment and in some instances reacted under pressure. The catalytic material in this process step is preferably a clay catalyst but other materials such as t-butyl peroxide can be used. Additionally, lithium carbonate can be added to enhance the polymerization reaction. Typically, the clay catalyst is present in a range of from 1 to 4.7% by weight of the fatty acid. If t-butyl peroxide is used, it is present in stoichiometric amounts to the polyunsaturated components and if lithium carbonate is used is added in a range of 0.1 to 0.15% by weight of the fatty acid.
In the polymerization step, if a clay catalyst is used the mixture is preferably reacted under pressure up to 55 PSI at temperatures in the range of 170 to 190xc2x0 C. for up to 6 hours. If t-butyl perxoide is used the mixture is further reacted at temperatures in the range of 120 to 135xc2x0 C.
After polymerization the mixture is cooled to at least 130xc2x0 C. If the polymerization process included the clay catalyst, phosphoric acid and/or diatomaceous earth elements are added to the cooled mixture and then filtered to remove the clay materials.
Finally, the oleic acid and lineloic dimer/trimer acids are separated from the reaction mixture using conventional separation techniques. Such separation techniques include a thin film evaporator or distillation columns. Generally, at least 50% oleic acid, typically over 60%, and preferably over 70%, is isolated by the invention process. The oleic acid isolated by this method has iodine values in the range of 80-100. Therefore, the oleic acid can be tailored depending on end use applications. Lower iodine values are preferred in applications where greater oxidative stability is required. Higher iodine values are preferred in applications where low temperature properties are desired.
Other objects, features and advantages of the present invention will be apparent when the detailed description of the preferred embodiments of the invention are considered with reference to the drawings, which should be construed in an illustrative and not limiting sense as follows: The fatty acid starting material includes monounsaturated components including oleic acid, oleic acid isomers and non-conjugated linoleic acid. In general, the fatty acid is selected from tall oil fatty acids, vegetable fatty acids, animal fatty acids and marine fatty acids.